I vibed with the passage in your book about choosing an amniocentesis when you were pregnant with your son, despite a low-risk NIPT. I am in a similar situation now, and I worry that a 1-in-10,000 chance of a false negative is still too high for me to feel comfortable with, but when I asked my doctor about getting an amnio after a low-risk NIPT, she acted like I was crazy and cited the 1-in-100 miscarriage stat. I find your analysis that the true risk is more like 1 in 800 to be convincing. But I’m wondering — years later, what’s your current take on the risk vs. reward ratio here?
—Julia
When I was pregnant with Finn, the non-invasive prenatal testing (NIPT) options were just getting started. These technologies are really exciting. They use the fact that when you’re pregnant, some of the baby’s DNA floats around in your bloodstream. The NIPT procedure is able to screen for a number of chromosomal abnormalities by, basically, looking for imbalances in chromosomes that would indicate the baby doesn’t have the expected number of chromosomes. These tests can also detect gender: if there are some Y chromosomes floating around, it’s a boy.
As you correctly point out, though, this is a screening and not a diagnostic test. False negatives — where you are told the screen is normal but, in the end, your child has a chromosomal abnormality — are possible. They are rare, but we do see them in large data sets. When I was pregnant with Finn, we had a negative screen on an NIPT test but still chose to pursue further testing to be sure.
As I talk about extensively in Expecting Better, choices about prenatal testing are deeply wrapped up in personal preference. Many of the guidelines about who should get what kind of testing are based on a comparison of risks (say, the risk of miscarriage versus the risk of an abnormality), which is really not a decision approach that makes much sense at all. Depending on how you weigh the event of miscarriage versus the event of having a child with a chromosomal abnormality, you’ll make this choice differently.
To your particular situation: the 1-in-100 miscarriage stat for an amniocentesis is just wrong. The 1-in-800 number, or even lower, is appropriate. As to how you weigh this against the false-negative risk… I cannot help you! I made the choice to get an amniocentesis, and I think it was the right choice. My doctor also thought I was crazy, but by that point I had already written Expecting Better, so I think they may have understood that there was no point in trying to talk me out of it.
If you decide this is the right choice for you, just say it, and then try to ignore the pushback.
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I was recently told not to test for microdeletions on the NIPT when I requested it because my OB practice “doesn’t tend to” because of an allegedly high false positive rate (I don’t know if this is accurate) and the follow up amniocentesis is “so dangerous” ( I know this to be inaccurate based on Expecting Better thank you!). I insisted on microdeletions anyway and when I got the results back, they had only ordered a test for one of them vs the four others available. I’m SO mad and it’s hard not to assume they don’t want me to test for microdeletions because they don’t want me to do anything with the information (I’m in Texas and this is a catholic OB practice). Needless to say, and apart from this incident anyway, I am switching providers! I may or may not write them a letter explaining why.